The present invention relates to a technique that carries out bidirectional, reciprocating main scan to prints an image on a printing medium. More specifically the present invention pertains to a technique that adjusts misalignment of dot recording positions in a main scanning direction between a forward pass and a backward pass of the main scan.
Recently color printers having a print head that ejects a plurality of different color inks have been widely used as an output device of computers. Some of such color printers have the function of xe2x80x9cbidirectional printingxe2x80x9d for the purpose of enhanced printing speed.
In bidirectional printing, misalignment of recording positions in a main scanning direction between a forward pass and a backward pass of main scan often arises due to backlash of a driving mechanism in the main scanning direction or a warp of a platen that supports a printing medium thereon. One of the known techniques proposed to relieve such positional misalignment is disclosed in JPA 5-69625 filed by the applicant of the present invention. This prior art technique registers in advance a potential amount of positional misalignment (deviation in printing) in the main scanning direction and adjusts the dot recording positions on the forward pass and on the backward pass, based on the registered amount of positional misalignment.
One of the applicable methods to adjust the recording positions in the main scanning direction actually prints a specific test pattern on the printing medium, and specifies the amount of positional misalignment in the main scanning direction based on the printed result of the specific test pattern, so as to determine the correction value. The process of printing the specific test pattern to specify the amount of positional misalignment generally accompanies sub-scan. The sub-scan feed may, however, cause deviation of the dot recording positions in the main scanning direction, due to backlash of a sub-scan driving mechanism or any inclined feed of the printing medium. The greater feeding amount and the greater number of feeds in the sub-scanning direction generally cause more significant misalignment of recording positions. Namely a large number of feeds in the sub-scanning direction by a large feeding amount in the process of printing the specific test pattern to specify the amount of positional misalignment in the main scanning direction undesirably causes error due to the sub-scan feed to be reflected on the printed result. This makes it difficult to accurately specify the amount of positional misalignment in the main scanning direction.
The object of the present invention is to solve the problem of the prior art technique discussed above and accordingly to provide a technique that relieves positional misalignment in the main scanning direction between a forward pass and a backward pass of main scan with regard to a nozzle array in a bidirectional printing apparatus.
In order to attain at least part of the above and the other related objects, one technique of the present invention prints positional misalignment test pattern with a nozzle group without sub-scan feed. The technique determines a correction value according to correction information that represents a favorable correction state selected based on the printed positional misalignment test pattern, and then actually corrects misalignment of recording positions in a main scanning direction occurring in bidirectional printing, using the correction value thus determined.
The sub-scan feed in the course of printing the xe2x80x9cpositional misalignment test patternxe2x80x9d causes working error of each mechanism relating to the sub-scan feed to be reflected on the printed xe2x80x9cpositional misalignment test pattern.xe2x80x9d This makes the correction value include some error. The arrangement of the present invention, however, prints the xe2x80x9cpositional misalignment test patternxe2x80x9d without any feed in the sub-scanning direction, thus preventing any such problem. This arrangement thus enables the correction value to be determined accurately, based on the properly printed xe2x80x9cpositional misalignment test pattern.xe2x80x9d
Another technique of the present invention prints a front test sub-pattern with a front nozzle sub-group on a printing medium on a selected one of the forward pass and the backward pass of the main scan of the print head. Here the front nozzle sub-group is part of the nozzle group and includes nozzles located in a relatively forward section of the nozzle group in a sub-scanning direction. The technique also prints a rear test sub-pattern with a rear nozzle sub-group on the printing medium on the other of the forward pass and the backward pass of the main scan of the print head. Here the rear nozzle sub-group is part of the nozzle group and includes nozzles located in a relatively backward section of the nozzle group in the sub-scanning direction. The technique subsequently determines a correction value according to correction information that represents a favorable correction state selected based on positional misalignment test pattern. Here the positional misalignment test pattern includes the rear test sub-pattern and the front test sub-pattern printed at different positions shifted in the sub-scanning direction. The technique then actually corrects using the correction value the misalignment of recording positions in the main scanning direction occurring in bidirectional printing thus determined. The xe2x80x9cforward (section) in the sub-scanning directionxe2x80x9d represents a direction from the print head, which moves relative to the printing medium, to the part of the printing medium that has not yet scanned by the print head. The xe2x80x9cbackward (section) in the sub-scanning directionxe2x80x9d is just opposite to the xe2x80x9cforward (section) in the sub-scanning direction.xe2x80x9d
This arrangement of the present invention enables the rear test sub-pattern and the front test sub-pattern, which are shifted in the sub-scanning direction, to be printed without any feed of the print head in the sub-scanning direction. The resulting xe2x80x9cpositional misalignment test patternxe2x80x9d is thus printed with little error and enables the user to readily select a favorable correction state and accurately determine the correction value according to the selected favorable correction state. In the above application, the xe2x80x9cpositional misalignment test patternxe2x80x9d is printed without any feed of the print head in the sub-scanning direction. One modified application may print the xe2x80x9cpositional misalignment test patternxe2x80x9d with small feeds in the sub-scanning direction, for the purpose of facilitating the determination of the correction value.
The following configuration is preferable when the nozzle group includes a low density nozzle group that forms only noncontiguous dots in the sub-scanning direction at a predetermined recording density on the printing medium by one pass of the main scan. The memory stores a first correction value therein, where the first correction value is used to correct misalignment of recording positions in the main scanning direction on the forward pass and the backward pass of the main scan with regard to the low density nozzle group. The first correction value is determined according to correction information that represents a favorable correction state selected based on a first positional misalignment test pattern. Here the first positional misalignment test pattern includes a first front test sub-pattern and a first rear test sub-pattern printed with the low density nozzle group at different positions shifted in the sub-scanning direction. The first front test sub-pattern includes a plurality of vertical ruled lines that extend in the sub-scanning direction and are formed using a first front nozzle sub-group by repeatedly carrying out a selected one of the forward pass and the backward pass of the main scan of the print head in combination with sub-scan feeds interposed between the main scan passes. Here the first front nozzle sub-group is part of the low density nozzle group and includes nozzles located in a relatively forward section of the low density nozzle group in the sub-scanning direction. The first rear test sub-pattern includes a plurality of vertical ruled lines that extend in the sub-scanning direction and are formed using a first rear nozzle sub-group by repeatedly carrying out the other of the forward pass and the backward pass of the main scan of the print head in combination with sub-scan feeds interposed between the main scan passes. Here the first rear nozzle sub-group is part of the low density nozzle group and includes nozzles located in a relatively backward section of the low density nozzle group in the sub-scanning direction. In this application, the printing apparatus may have a plurality of the low density nozzle groups, and the memory may store a plurality of the first correction values.
In this application, the xe2x80x9cfirst rear test sub-patternxe2x80x9d and the xe2x80x9cfirst front test sub-patternxe2x80x9d respectively consist of vertical ruled lines of contiguous dots in the sub-scanning direction. The xe2x80x9cfirst correction valuexe2x80x9d, which is used to correct the misalignment of recording positions in the main scanning direction, is thus readily determined, based on the xe2x80x9cfirst rear test sub-patternxe2x80x9d and the xe2x80x9cfirst front test sub-pattern.xe2x80x9d This printing process accompanies some feeds in the sub-scanning direction to make the dots contiguous in the sub-scanning direction. But no large feeds in the sub-scanning direction are required to print the xe2x80x9crear test sub-patternxe2x80x9d and the xe2x80x9cfront test sub-patternxe2x80x9d at the different positions shifted in the sub-scanning direction. The resulting xe2x80x9cpositional misalignment test patternxe2x80x9d is printed with little error and enables the user to accurately determine the correction value based on the printed xe2x80x9cpositional misalignment test pattern.xe2x80x9d
It is preferable that the feeding amount of sub-scan in printing the first positional misalignment test pattern is equal to one dot pitch. The feeds in the sub-scanning direction by one dot between the consecutive passes of the main scan enable continuous dots to be printed even with the low density nozzle group that creates only noncontiguous dots in the sub-scanning direction by one pass of the main scan. The feed in the sub-scanning direction is the one dot space, so that the xe2x80x9cpositional misalignment test patternxe2x80x9d can be printed with a small summation of the feeds in the sub-scanning direction. This reduces the error of the feed in the sub-scanning direction. The resulting xe2x80x9cpositional misalignment test patternxe2x80x9d is thus printed with little error and enables the user to accurately determine the correction value based on the printed xe2x80x9cpositional misalignment test pattern.xe2x80x9d
The following configuration is preferable when the nozzle group includes a high density nozzle group that forms contiguous dots in the sub-scanning direction at a predetermined recording density on the printing medium by one pass of the main scan. The memory stores a second correction value therein, where the second correction value is used to correct misalignment of recording positions in the main scanning direction on the forward pass and the backward pass of the main scan with regard to the high density nozzle group. The second correction value is determined according to correction information that represents a favorable correction state selected based on a second positional misalignment test pattern. Here the second positional misalignment test pattern includes a second front test sub-pattern and a second rear test sub-pattern printed with the high density nozzle group at different positions shifted in the sub-scanning direction. The second front test sub-pattern includes a plurality of vertical ruled lines of continuous dots that extend in the sub-scanning direction and are formed using a second front nozzle sub-group on a selected one of the forward pass and the backward pass of the main scan of the print head. Here the second front nozzle sub-group is part of the high density nozzle group and includes nozzles located in a relatively forward section of the high density nozzle group in the sub-scanning direction. The second rear test sub-pattern includes a plurality of vertical ruled lines of continuous dots that extend in the sub-scanning direction and are formed using a second rear nozzle sub-group on the other of the forward pass and the backward pass of the main scan of the print head. Here the second rear nozzle sub-group is part of the high density nozzle group and includes nozzles located in a relatively backward section of the high density nozzle group in the sub-scanning direction. The second positional misalignment test pattern is printed without sub-scan feed.
In this application, the nozzle group can form contiguous dots in the sub-scanning direction at a predetermined recording density on the printing medium by one pass of the main scan. In this arrangement, the printing apparatus can print the xe2x80x9csecond rear test sub-patternxe2x80x9d and the xe2x80x9csecond front test sub-patternxe2x80x9d, which respectively include vertical ruled lines extending in the sub-scanning direction, without any feed of sub-scan. The resulting xe2x80x9cpositional misalignment test patternxe2x80x9d is thus printed with little error and enables the user to determine the correction value accurately according to the positional misalignment test pattern.
In accordance with one preferable embodiment, the misalignment of recording positions in the main scanning direction occurring in bidirectional printing, is corrected using a mean of the first correction value and the second correction value. In this embodiment, there may be a plurality of the low density nozzle groups and a plurality of the high density nozzle groups.
The technique of the embodiment carries out proper correction, based on both the first correction value, which reflects the characteristics of the low density nozzle group, and the second correction value, which reflects the characteristics of the high density nozzle group. The arrangement carries out the correction with the mean of the first correction value and the second correction value. This enables the characteristics of both the low density nozzle group and the high density nozzle group to be readily reflected on the correction.
In accordance with one preferable application, the high density nozzle group ejects black ink and the low density nozzle group includes a plurality of chromatic color nozzle groups, where each chromatic color nozzle group ejects a chromatic color ink. In this application, the first correction value is determined individually for at least one chromatic color nozzle group selected among the plurality of chromatic color nozzle groups. The positional misalignment correction unit may correct the misalignment of recording positions in the main scanning direction occurring in bidirectional printing using a mean of at least two correction values selected out of the second correction value and the at least one first correction value determined for the at least one selected chromatic color nozzle group, in a specific print mode in which nozzles in the low density nozzle group are used.
In the case of color printing with the low density nozzle group, the misalignment of recording positions can be readily corrected using the mean of the first correction values and the second correction value. Each of the first correction values reflects the characteristics of each chromatic color nozzle group, and the second correction value reflects the characteristics of the high density nozzle group ejecting black ink. The chromatic color nozzle groups that are taken into account for and added to the calculation of the xe2x80x9cmeanxe2x80x9d may be selected based on the position of nozzles in the chromatic color nozzle group and the conspicuousness of the misalignment of recording positions by the nozzle group. This ensures correction suitable for color printing. The xe2x80x9cchromatic color nozzle groupxe2x80x9d of which the first correction value is set may be the same chromatic color nozzle groups that are taken into account for and added to the calculation of the xe2x80x9cmean.xe2x80x9d
In accordance with another preferable application, the first correction value is determined for at least one chromatic color nozzle group selected among the plurality of chromatic color nozzle groups. The positional misalignment correction unit may correct the misalignment of recording positions using one of the first correction value in a specific print mode in which nozzles in the low density nozzle group are used.
In the case of color printing with the low density nozzle group, this application corrects the misalignment of recording positions using the first correction value, which reflects the characteristics of one chromatic color nozzle group included in the low density nozzle group. This chromatic color nozzle group may be appropriately selected by considering the position of nozzles in the chromatic color nozzle group and the conspicuousness of the misalignment of recording positions by the chromatic color nozzle group. This ensures correction suitable for color printing.
In accordance with still another preferable application, the high density nozzle group ejects black ink, and the low density nozzle group includes a plurality of chromatic color nozzle groups, where each chromatic color nozzle group ejects a chromatic color ink. The positional misalignment correction unit may correct the misalignment of recording positions using the second correction value in a specific print mode in which nozzles in the low density nozzle group are not used. In the case of monochromatic printing, this application carries out correction with the second correction value, which reflects the characteristics of the high density nozzle group. This accordingly ensures adjustment of recording positions suitable for monochromatic printing.
In accordance with another preferable application, the positional misalignment correction unit may correct the misalignment of recording positions using the first correction value with regard to the low density nozzle group, and using the second correction value with regard to the high density nozzle group. This arrangement ensures the correction optimum for both the low density nozzle group and the high density nozzle group in the course of one identical printing operation.
The present invention is realized by a diversity of applications as given below:
(1) Bidirectional printing apparatus;
(2) Method of bidirectional printing;
(3) Method of correcting misalignment of recording positions in the course of bidirectional printing;
(4) Computer programs for implementing any of the above apparatus and methods;
(5) Recording media in which computer programs for implementing any of the above apparatus and methods is recorded; and
(6) Data signals that include computer programs for implementing any of the above apparatus and methods and are embodied in carrier waves.
FIG. 1 schematically illustrates the structure of a printing system including an ink jet printer 20 in a first embodiment;
FIG. 2 is a block diagram showing the structure of a control circuit 40 included in the printer 20;
FIG. 3 shows plural actuator chips and plural nozzle arrays provided on the print head 28;
FIG. 4 is a flowchart showing a procedure of determining a correction value based on a test pattern;
FIG. 5 is a block diagram illustrating the main configuration relating to correction of positional misalignment in bidirectional printing in the first embodiment.;
FIG. 6 shows a method of determining the correction value used for adjusting the positional misalignment, based on a test pattern in the first embodiment;
FIG. 7 shows another method of determining the correction value used for adjusting the positional misalignment, based on a test pattern in a second embodiment;
FIG. 8 shows the method of determining the correction value used for adjusting the positional misalignment, based on the test pattern in the second embodiment; and
FIG. 9 is a block diagram illustrating the main configuration relating to the correction of positional misalignment in bidirectional printing in a third embodiment.